From dd907c2d86eaaad0910e7bfe3f0d25e5caf8bdf7 Mon Sep 17 00:00:00 2001
From: Hsiang-Ying Fu <66062782+fuhsnn@users.noreply.github.com>
Date: Sat, 26 Sep 2026 06:35:22 +0800
Subject: Extend and backport SubNode peephole (#254)

* Extend and backport SubNode peephole

* Add tests

* Restrict subtraction zero peepholes to integer operands

Require resolved integer mode in chapter 25 so zero subtraction preserves floating-point signed zero. Keep nonnumeric operands in the graph for subtraction diagnostics.

Add signed-zero coverage from chapter 12 and null-subtraction diagnostics from chapter 22. Confirmed the regressions fail on the original PR. Full Make suites pass in chapters 4-25 (5462 tests), including fresh chapter 25 sys.o compilation.

---------

Co-authored-by: Cliff Click <cliffc@acm.org>
---
 .../java/com/seaofnodes/simple/Chapter04Test.java  | 28 ++++++++++++++++++++++
 .../java/com/seaofnodes/simple/Chapter12Test.java  |  7 ++++++
 2 files changed, 35 insertions(+)

(limited to 'chapter21/src/test/java/com')

diff --git a/chapter21/src/test/java/com/seaofnodes/simple/Chapter04Test.java b/chapter21/src/test/java/com/seaofnodes/simple/Chapter04Test.java
index c6199193..e5a16680 100644
--- a/chapter21/src/test/java/com/seaofnodes/simple/Chapter04Test.java
+++ b/chapter21/src/test/java/com/seaofnodes/simple/Chapter04Test.java
@@ -52,6 +52,34 @@ public class Chapter04Test {
         assertEquals("return arg;", code.print());
     }
 
+    @Test
+    public void testSub0() {
+        CodeGen code = new CodeGen("return arg-0;");
+        code.parse();
+        assertEquals("return arg;", code.print());
+    }
+
+    @Test
+    public void test0Sub() {
+        CodeGen code = new CodeGen("return 0-arg;");
+        code.parse();
+        assertEquals("return (-arg);", code.print());
+    }
+
+    @Test
+    public void testSubNeg() {
+        CodeGen code = new CodeGen("return 3--arg;");
+        code.parse();
+        assertEquals("return (arg+3);", code.print());
+    }
+
+    @Test
+    public void testNegSub() {
+        CodeGen code = new CodeGen("return -arg-3;");
+        code.parse();
+        assertEquals("return (-(arg+3));", code.print());
+    }
+
     @Test
     public void testVarArg() {
         CodeGen code = new CodeGen("return arg; ");
diff --git a/chapter21/src/test/java/com/seaofnodes/simple/Chapter12Test.java b/chapter21/src/test/java/com/seaofnodes/simple/Chapter12Test.java
index 21759b78..c50be559 100644
--- a/chapter21/src/test/java/com/seaofnodes/simple/Chapter12Test.java
+++ b/chapter21/src/test/java/com/seaofnodes/simple/Chapter12Test.java
@@ -7,6 +7,13 @@ import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.fail;
 
 public class Chapter12Test {
+    @Test public void testSubZeroFloat() {
+        var code = new CodeGen("flt x = arg; return 0-x;").parse().opto().typeCheck();
+        // Compare strings so +0.0 and -0.0 remain distinct.
+        assertEquals("0.0", Eval2.eval(code,0));
+        assertEquals("-1.0", Eval2.eval(code,1));
+    }
+
     @Test public void testDeadNumericReturns() {
         for( String[] test : new String[][] {
             {"if(1) return 7; else return 2.5;", "7"},
-- 
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